Boss power up on/off state

[flintstoned]

looking for help with my boss effects. some are on when powered up (GE7 & MT2), some are off (NS2). when i flip the switch on to fire up my rig, i would like the exact opposite on these. i found a thread about this on the boss forum but it kinda died out before anyone figured out the proper way to change it. they had talked about swapping the two 56k resistors (R38 & R39) going to 9v. I tried this and although there was a small difference between them due to the tolerances (55.4k vs. 54.8k) it didnt change the power up state. they also talked about swapping the transistors, but the cheap traces on these boards dont give you too many chances for trial and error, so i brought it to the pros, any ideas?

[The Tone God]

I wrote this awhile ago which may help.

http://www.thetonegod.com/tech/state/state.html

Andrew

[Processaurus]

That's an interesting article, especially because the bulletproof solution isn't as simple as one might guess.  It is a crazy thing, though, playing live, and if anything happens to the power for an instant (like the daisy chain shorts on a pedal's chassis, or bass player rocks out and steps on the adapter, etc.)  all the pedals reset into whatever random state they like to be in.  A battery backed circuit that remembers its bypass state when the power is off would be the bees knees!

[amptramp]

This solves the problem of switch debouncing using an SPDT switch and the output is initialized on turn-on:



The outputs from the Q and /Q of U1-B go through R-C networks to achieve slow, silent switching of the FETs used for signal switching.  The Q output goes to a transistor (either bipolar or FET) used as an inverter to drive the indicator LED.  This meets all the criteria you need:

1. The switch is initialized with Q low and /Q high.
2. There is no effect from switch bounce - one switch push alternates the output lines once.
3. The circuit can be extended to 9 VDC operation by using a 74C74 in place of an HC.
4. The circuit operates down to 2 volts and takes very little power, mainly through the resistor pullup used for the switch.
5. Changing the normally closed and normally open contacts changes from switching when the switch is pushed to switching when the switch is released.
6. The use of a series resistor and capacitor to ground ensures that the switch operation is gradual so that there is no switch pop due to sudden transfer from one input to the other.
7. The diode across the initialize capacitor ensures rapid return to the initialize state on power removal.

This takes a long time to load from TinyCAD to photobucket and then to copy here, so I hope I got it right the first time!

[slotbot]

you shoudl be able to do it by decreasing  (or increasing) the value of a resistor in either of these 2 pairs: (R38, R39) or(R41, R42)

Its some sort of bistable latch circuit, so it flips from on to off or off to on. The problem is on power up it is neither off or on so the state will be determined by which capacitor at the base of the transistors charges first. I cant see the rest of the schematic so i dont know which transistor/signal is making it on or bybass but for example the path from Vcc through R38 and R41 will charge C30 and the path through R39 and R42 will charge C31.

If you decrease R39 or R42 C31 should charge faster than C30.

You should be able to make what you want happen without adding anything and just tweaking the R values.

[flintstoned]

Thanks for the input! Thought I'd try the easiest idea first. Tried a 47k first, no difference, remembering in the other thread bout a dude getting a 33k to work but had squealing so I went the other way and put a 100k in there and that did the trick. Rc time constant lesson: when i was testing it out and toggling power on and off,i noticed if i toggle too fast it wasnt always the same result. I assume a cap didnt have enough time to discharge. But in the end they fire up in the state i want when i fire up my rig. Of course on both pedals I wanted to change, I chose the wrong resistor first and got the opposite of what I wanted and had to desolder then swap the two around, losing half a solder pad in the process. tis the way my diy's like to go!

[Rob Strand]

I'd try adjusting the 56k resistors R37/R40, reducing one to 47k should do it.  If not try reducing one to 47k and increasing the other to 68k.   Suggestions beyond that, which didn't produce unwanted behaviors (when the battery is low for example ) would require a more detailed analysis.

The idea is to create an asymmetry in the turn-on thresholds.